Grate assembly

ABSTRACT

A grate assembly for guiding air into a pile of combustible wood pellets for combustion thereof. The grate assembly includes a structural subassembly having at least two sets of elongate members, a first one of the two sets forming a lower layer for at least partially supporting a second one of the two sets forming an upper layer. The grate assembly also includes a support element attached to the structural subassembly. Each member includes a body at least partially defining one or more channels and a number of holes in fluid communication with the channel(s) to guide air into the pile of the wood pellets. The support element includes a base portion with a plurality of apertures, for ignition of the pellets therethrough

This application is a continuation-in-part application of prior application Ser. No. 12/411,545, filed Mar. 26, 2009. This application hereby claims priority from such prior application and incorporates such prior application in its entirety by reference.

FIELD OF THE INVENTION

This invention is related to a grate assembly for guiding air into a pile of wood pellets for combustion thereof.

BACKGROUND OF THE INVENTION

Wood pellets, primarily made of compacted sawdust and wood chips, are commonly used as fuel in various burner and/or stove devices. The pellets are generally cylindrical or round and relatively small (e.g., between about ¼ and 1½ inches long, and about ¼ inch in diameter). The pellets typically have water content of less than about 10 percent. During the formation of the pellets under pressure, lignin in the sawdust and wood chips plastifies to a limited extent, and the lignin serves to hold the pellet materials together. With increases in the costs of various fossil fuels, wood pellets are a viable heat energy source, whether supplementary or otherwise.

Because the wood pellets are relatively small, a large number is required in order to result in a substantial fire. Pellet stoves or burners are known in which the pellets are fed (typically by an auger) into a burner portion thereof from a hopper. The user puts a relatively large amount of pellets into the hopper, and the auger conveys the pellets to the burner portion from the hopper. The burner portion in such a stove is designed solely to burn pellets, and may include a substantially horizontal plate with holes therein. The pellet stove typically also includes a fan positioned below the plate, for blowing air upwardly at the plate and, to an extent, through the holes. Because of this forced circulation of air in the burner portion, some pellets positioned on the plate are relatively completely burned, however, many are not.

Many people would like to use a wood stove that they already own instead of expending a significant expense in purchasing a pellet stove. In a traditional wood stove, however, the combustion of a pile of wood pellets tends to be incomplete at best. The incomplete combustion results from poor circulation of air throughout the pile.

SUMMARY OF THE INVENTION

For the foregoing reasons, there is a need for a grate assembly which overcomes or mitigates one or more of the defects of the prior art.

In its broad aspect, the invention provides a grate assembly for guiding air into a pile of combustible wood pellets for combustion thereof. The grate assembly includes a structural subassembly having at least two sets of elongate members, a first one of the two sets forming a lower layer for at least partially supporting a second one of said at least two sets forming an upper layer. Each member includes a body at least partially defining one or more channels and a number of holes in fluid communication with the channel(s) to guide air from the channel into the pile of the wood pellets. The members are spaced apart from each other in a predetermined arrangement to distribute air into the pile of the wood pellets. The grate assembly also includes one or more support elements attached to the structural subassembly. The support element has a base portion with a plurality of apertures, for ignition of the pellets therethrough.

In another of its aspects, the invention includes a grate assembly for guiding air into a pile of combustible wood pellets for combustion thereof, in which the support element at least partially retains at least a portion of the pile of combustible wood pellets on the structural subassembly.

In yet another of its aspects, the invention provides a grate assembly adapted to be positioned in a firebox at least partially defined by a rear wall and a front wall having an opening, for guiding air into a pile of combustible wood pellets for combustion thereof. The grate assembly includes a structural subassembly comprising at least two sets of elongate members, a first one of the two sets forming a lower layer for at least partially supporting a second one of the two sets forming an upper layer. Each member includes a body at least partially defining one or more channels and a number of holes in fluid communication with the channel(s) to guide said air from the channel into the pile of the wood pellets. The members are spaced apart from each other in a predetermined arrangement to distribute the air into the pile of the wood pellets. The grate assembly also includes one or more support elements attached to the structural subassembly. The support element has a base with a number of apertures, for ignition of the pellets therethrough. The structural subassembly is positionable in the firebox so that the support element is accessible via the opening in the front wall.

In another aspect, the invention provides a stove with a firebox in which the grate assembly is positioned.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with reference to the attached drawings, in which:

FIG. 1A is an isometric view of an embodiment of the grate assembly of the invention;

FIG. 1B is an isometric view of a portion of the grate assembly of FIG. 1A, drawn at a larger scale;

FIG. 2 is an isometric view of another portion of the grate assembly of FIG. 1A, drawn at a larger scale;

FIG. 3 is a side view of the grate assembly of FIG. 1A with wood pellets positioned therein and thereon, drawn at a smaller scale;

FIG. 4 is another side view of the grate assembly of FIG. 3;

FIG. 5 is a top view of an embodiment of the grate assembly of the invention, drawn at a smaller scale; and

FIG. 6 is a cross-section of an embodiment of a stove of the invention, drawn at a smaller scale.

DETAILED DESCRIPTION

Although other applications may be envisioned for the present invention, the application of the present invention is particularly advantageous for efficiently burning wood pellets. It will be appreciated by one skilled in the art that the present invention may also be used to burn pellets made of other biomaterials such as corn, switchgrass, or organic waste. Accordingly, without intending to limit the present invention to the embodiments described herein, the invention will be described below in further detail having regard to the system and in particular the varied assortment and arrangement of devices used in that system as shown in the attached drawings.

Reference is made to FIGS. 1A-5 to describe an embodiment of a grate assembly in accordance with the invention indicated generally by the numeral 20. The grate assembly 20 is for guiding air into a pile 22 of combustible wood pellets 24 for combustion thereof (FIGS. 3, 4). The grate assembly 20 preferably includes a structural subassembly 26 with at least two sets 20 of elongate members 30. Preferably, a first one of the sets forms a lower layer 28 a for at least partially supporting a second one of the sets forming an upper layer 28 b (FIG. 4), as will be described. Each member 30 preferably includes a body 32 at least partially defining a channel 34 and including a number of holes 36 in fluid communication with the channel 34 to guide the air from the channel 34 into the pile 22 of the wood pellets 24 (FIGS. 3, 4). Preferably, the members 30 are spaced apart from each other in a predetermined arrangement for distribution of the air into the pile 22 of the wood pellets 24. It is also preferred that the grate assembly 20 includes one or more support elements 38 attached to the structural subassembly 26. As can be seen in FIG. 1B, the support element 38 preferably includes a base portion 40 having a number of apertures 42, for ignition of the pellets 24.

As can be seen in FIGS. 1A, 3, and 4, the channel 34 of each member 30 preferably extends along the body 32 thereof. It is also preferred that the elongate members 30 in each set 28 are positioned substantially parallel to each other (FIG. 1A). The adjacent layers preferably are positioned so that the members therein are substantially orthogonal to each other. This arrangement provides certain benefits. First, as well as lateral (i.e., horizontal) distribution of air through the pile at the level of each layer, a portion of the air guided into the pile at one level rises (i.e., is vertically distributed also), to be captured in members of higher levels and guided thereby further. Second, the regular arrangement of the elongate members provides for relatively even (i.e., both lateral and vertical) distribution of air throughout the pile of wood pellets.

Those skilled in the art would appreciate that the body 32 may be formed in various ways, of a variety of materials. Preferably, each body is formed of any suitable material or materials, i.e., any material or materials that can withstand the relatively high temperatures due to combustion of the wood pellets over a considerable period of time without significantly degrading.

In one embodiment, the body 32 of each member 30 preferably includes two planar segments 44, 46 connected to define an apex 48 thereof (FIG. 1B). As can be seen in FIG. 1B, each member 30 preferably is positioned with the apex 48 thereof oriented substantially upwardly. It has been found that stainless steel is a suitable material out of which the body may be made. Preferably, each set 28 is affixed to one or more other sets at one or more contact points 50. The sets may be attached to each other in any suitable manner. Each set 28 preferably is attached to the adjacent set(s) thereto by welding. The welding joints preferably are formed at the contact points 50.

As indicated above, the grate assembly may be made of various materials. For example, the grate assembly may be integrally formed of a suitable ceramic.

In one embodiment, the support element 38 includes a substantially vertical portion 52 extending upwardly from the base portion 40. As will be described, the substantially vertical portion 52 is for retaining at least a portion of the pile 22 on the grate assembly 20.

As can be seen in FIGS. 1A-4, although the grate assembly 20 may have as few as two layers 28 of members 30, it is preferred that the assembly 20 includes more such layers, e.g., three or four layers. In FIGS. 3 and 4, the sets or layers are identified as 28 a-28 d, from bottom to top respectively, for clarity of illustration. Those skilled in the art will appreciate that any suitable number of sets or layers may be used.

Preferably, the support element 38 is attached in any suitable manner to the structural subassembly 26. As shown in FIGS. 2 and 3, for instance, the base portion 40 may be attached to the apexes of the members in the second set or layer 28 b. It is preferred that the top set 28 d is positioned relative to the support element 38 so that the portion 52 extends above the apexes of the members in the top layer 28 d by a predetermined distance “D” (FIG. 3), so that the portion 52 retains at least part of the pile 22 on the structural subassembly 26.

In use, and as shown in FIG. 5, the grate assembly 20 preferably is positioned in a firebox 60. As can be seen in FIG. 5, the firebox 60 is at least partially defined by a rear wall 62 and a front wall 64 having an opening 66 therein, and by side walls 68, 70 extending between the rear and front walls 62, 64. Preferably, the structural subassembly 26 is positioned in the firebox 60 so that the support element 38 is accessible via the opening 66 in the front wall 64. The support element 38 preferably is positioned proximal to the opening 66. It will be understood that, once the grate assembly 20 is positioned in the firebox as shown in FIG. 5, the wood pellets are piled onto the grate assembly 20, to form the pile 22 as shown in FIGS. 3 and 4.

From FIGS. 3-5, it can be seen that, when the grate assembly 20 is positioned in the firebox 60 with the support element 38 proximal to the opening, a user (not shown) can ignite the wood pellets 24 through the apertures 42 in the base 40. This is advantageous because the wood pellets positioned above the apertures can be relatively easily ignited, due to their raised position, which permits a flame (e.g., from a match) to be held close to such pellets. In the absence of the support element, the user would be required to find wood pellets appropriately positioned for ignition.

Because of the positioning of the members (i.e., with apex up), air is distributed in the pile 22 of wood pellets 24 via the members 30. As is well known in the art, when combustion begins, relatively hot combustion flue gases are generated by the combustion, and these rise because they are hotter than the ambient air surrounding the pile. This causes air to flow into the pile through the channels 34, ultimately leading to combustion throughout the pile.

When combustion of the wood pellets is taking place, air is drawn into the members, as schematically represented by arrows “A” in FIG. 5. Also, air moving along the channel 34 is released from the channel 34 via the holes 36, as schematically represented by arrows “B” in FIGS. 3 and 5. Those skilled in the art will appreciate that the movement of air through the holes 36 as schematically represented in FIG. 5 is generally somewhat diffuse, i.e., such movement is generally in more than one direction, notwithstanding that such movement is schematically represented in FIG. 5 by single arrows. It can be seen, therefore, that air is distributed generally throughout the pile of wood pellets through the grate assembly, to result in substantially complete combustion of the pile of wood pellets 24.

It will be appreciated by those skilled in the art that the support element 38 advantageously retains at least a portion of the pile 22. As can be seen in FIG. 3, some of the wood pellets 24 are held in position on the grate assembly 20 by the support element 38. Accordingly, because of the support element 38, the pile 22 can be formed to have a relatively steep profile at its front side, i.e., the side of the pile positioned proximal to the opening 66. Piling the wood pellets 24 higher is advantageous because it tends to result in more combustion, due to more pellets being vertically positioned relative to each other.

Those skilled in the art will appreciate that, in general, combustion of the pile of wood pellets is faster and more complete when the grate assembly and the pile of wood pellets are positioned in a stove designed for burning wood (i.e., and partially sealed) or a fireplace which is partially sealed, so that the temperature inside the firebox is maintained at a relatively high temperature once combustion of the pile is well underway. Advantageously, the grate assembly of the invention distributes air throughout the pile of wood pellets without requiring a motor-driven fan, in contrast to the typical stove designed for pellet burning. Also, it has been found that ignition of the pile of wood pellets is best accomplished by using a small amount of a suitable “fire-starter” petroleum product.

As can be seen in FIG. 6, in one embodiment, the invention preferably includes a stove 72 including the firebox 60 and the grate assembly 20 positioned in the firebox 60.

It will be appreciated by those skilled in the art that the invention can take many forms, and that such forms are within the scope of the invention as described above. The foregoing descriptions are exemplary, and their scope should not be limited to the preferred versions provided therein. 

1. A grate assembly for guiding air into a pile of combustible wood pellets for combustion thereof, the grate assembly comprising: a structural subassembly comprising at least two sets of elongate members, a first one of said at least two sets forming a lower layer for at least partially supporting a second one of said at least two sets forming an upper layer; each said member comprising a body at least partially defining at least one channel and comprising a plurality of holes in fluid communication with said at least one channel to guide said air from said at least one channel into the pile of the wood pellets; the members being spaced apart from each other in a predetermined arrangement to distribute said air into the pile of the wood pellets; at least one support element attached to the structural subassembly; and said at least one support element comprising a base portion with a plurality of apertures, for ignition of the pellets therethrough.
 2. A grate assembly according to claim 1 in which said at least one channel of each said elongate member extends along the body thereof.
 3. A grate assembly according to claim 1 in which the elongate members in each said set are positioned substantially parallel to each other.
 4. A grate assembly according to claim 1 in which the body of each said member comprises at least two planar segments connected to define an apex thereof.
 5. A grate assembly according to claim 4 in which each said member is positioned with the apex thereof oriented substantially upwardly.
 6. A grate assembly according to claim 4 in which each said set is affixed to at least one other said set at least one contact point.
 7. A grate assembly according to claim 6 in which each said set is affixed to the other said adjacent set by welding.
 8. A grate assembly according to claim 1 in which the grate assembly is integrally formed.
 9. A grate assembly for guiding air into a pile of combustible wood pellets for combustion thereof, the grate assembly comprising: a structural subassembly comprising at least two sets of elongate members, a first one of said at least two sets forming a lower layer for at least partially supporting a second one of said at least two sets forming an upper layer; each said member comprising a body at least partially defining at least one channel and a plurality of holes in fluid communication with said at least one channel to guide said air from said at least one channel into the pile of the wood pellets; the members being spaced apart from each other in a predetermined arrangement to distribute said air into the pile of the wood pellets; and at least one support element attached to the structural subassembly, for at least partially retaining at least a portion of the pile of combustible wood pellets on the structural subassembly.
 10. A grate assembly according to claim 9 in which said at least one support element comprises a base with a plurality of apertures, for ignition of the pellets therethrough.
 11. A grate assembly according to claim 9 in which said at least one channel of each said member extends along the body thereof.
 12. A grate assembly according to claim 9 in which the elongate members in each said set are positioned substantially parallel to each other.
 13. A grate assembly according to claim 9 in which the body of each said member comprises at least two planar segments connected to define an apex thereof.
 14. A grate assembly according to claim 13 in which each said member is positioned with the apex thereof oriented substantially upwardly.
 15. A grate assembly according to claim 13 in which each said set is affixed to the other adjacent set by welding.
 16. A grate assembly adapted to be positioned in a firebox at least partially defined by a rear wall and a front wall having an opening, for guiding air into a pile of combustible wood pellets for combustion thereof, the grate assembly comprising: a structural subassembly comprising at least two sets of elongate members, a first one of said at least two sets forming a lower layer for at least partially supporting a second one of said at least two sets forming an upper layer; each said member comprising a body at least partially defining at least one channel and a plurality of holes in fluid communication with said at least one channel to guide said air from said at least one channel into the pile of the wood pellets; the members being spaced apart from each other in a predetermined arrangement to distribute said air into the pile of the wood pellets; at least one support element attached to the structural subassembly, said at least one support element comprising a base with a plurality of apertures, for ignition of the pellets therethrough; and the structural subassembly being positionable in the firebox such that said at least one support element is accessible via the opening in the front wall.
 17. A grate assembly according to claim 16 in which said at least one support element at least partially retains at least a portion of the pile of combustible wood pellets on the structural subassembly.
 18. A stove with a firebox for combustion of combustible fuel therein comprising the grate assembly according to claim 1 positioned in the firebox. 